Buffer station with single exit-flow direction

ABSTRACT

A buffer for use in semiconductor processing tools is disclosed. The buffer may be used to temporarily store wafers after processing operations are performed on those wafers. The buffer may include two side walls and a back wall interposed between the side walls. The side walls and the back wall may generally define an area within which the wafers may be stored in a stacked arrangement. Wafer support fins extending from the side walls and the back wall may extend into a wafer support region that overlaps with the edges of the wafers. Purge gas may be introduced in between each pair of wafers via purge gas ports located in one of the walls.

BACKGROUND

Semiconductor processing operations are often performed in asemiconductor processing tool, which may feature several semiconductorprocessing chambers or reactors that are connected to a transfer chamberof some sort; the transfer chamber and the semiconductor processingchambers are typically connected together in a hermetically-sealedmanner and kept under vacuum conditions. Wafers are typically providedto, and removed from, the transfer chamber via loadlocks.

The loadlocks are typically connected to an Equipment Front End Module(EFEM), which is usually a structure with a wafer handling robot insidethat is configured to move wafers between the load locks and a number ofother structures within, or attached to, the EFEM. The internalenvironment of the EFEM is typically referred to as a“mini-environment”; filtered, dry air is typically constantly flowedthrough the mini-environment (it is not practical to keep the EFEM at avacuum, which is why loadlocks are used as a barometric interfacebetween the EFEM and the transfer chamber). Wafers are typicallysupplied to the EFEM using cassettes of vertically-stacked wafers (e.g.,25 or 30 wafers) called Front-Opening Unified Pods (FOUPs); the robot inthe EFEM may pick a wafer from a FOUP and transfer it to the loadlock,or may transfer processed wafers into a FOUP.

Industry standard processes typically mandate that a FOUP contain onlyunprocessed (and thus clean) wafers or contain only processed (andpotentially dirty) wafers—mixing unprocessed and processed wafers in asingle FOUP is considered undesirable and is against industry standardpractices. Moreover, wafers are often quite hot after they exitprocessing, and it may be undesirable to put hot wafers into the FOUPsuntil they are cooled down. To that end, an EFEM will often include abuffer or buffer station that may be used to temporarily storein-process wafers before they are transferred to the processed waferFOUP. Buffers typically hold a large number, e.g., 25 or 30, wafers in avertically-stacked arrangement.

Since the wafers that are stored in a buffer have usually undergonerecent semiconductor processing operations, they often have chemicalresiduals from the processing operations on their exposed surfaces.Moisture and oxygen in the mini-environment of the EFEM may react withsuch chemical residues, causing damage to the processed wafers and canalso damage the components of the buffer or EFEM near the wafers.

One technique for mitigating such chemical reactions is to use a buffersuch as is described in KR 1020140059574, published Jul. 6, 2013. Such abuffer includes two opposing, vertical stacks of plates that are atleast a wafer diameter apart. Small, short ledges extend fromalternating instances of such plates and provide a small support area onwhich each wafer may rest. These ledges extend around only a shortdistance of the wafer perimeter on opposing sides of the wafer, e.g.,around about ⅛^(th) of the wafer circumference on each opposing side. Aseries of vertical gas delivery tubes extends upwards through each plateinstance, and nozzles in each tube are used to direct purge gas out ofslots in alternating instances of the plates and towards the mid-planeof the wafers. The purge gas in this case flows towards the middle ofthe wafers as well as towards the front and the back of the wafer.

SUMMARY

The systems, methods and devices of the disclosure each have severalinnovative aspects, no single one of which is solely responsible for thedesirable attributes disclosed herein. One innovative aspect of thesubject matter described in this disclosure can be implemented in avariety of ways.

In some implementations, a buffer for storing multiple wafers in asemiconductor manufacturing tool is provided. The buffer may include twoopposing side walls, a back wall, and a plurality of support fins. Thetwo opposing side walls and the back wall may define part of an interiorbuffer volume which may have an opening opposite the back wall; theopposing side walls may be between the opening and the back wall. Eachsupport fin may extend from the back wall, along both side walls, and tothe opening. Each support fin may also be substantially flat andhorizontal when the buffer is in use and have a wafer support regionthat is smaller in diameter than the wafers with which the buffer isdesigned to be used. The support fins may also extend from the sidewalls and the back wall in a substantially unbroken manner up to atleast the wafer support region, and may have a cutout region thatextends from the opening past the center of the wafer support region andthat is wide enough in a direction transverse to the opening to allow anend effector of a wafer handling robot to place a wafer on the supportfin.

In some implementations, each support fin may be offset from theadjacent support fin or support fins and the support fins form avertical linear array when the buffer is in use.

In some implementations, the buffer may also include a ceiling and afloor. The interior buffer volume may be further defined by the ceilingand the floor and the back wall and the two sidewalls may be between theceiling and the floor.

In some such implementations, the opposing side walls, the back wall,the ceiling, and the floor may seal the interior buffer volume off fromthe surrounding environment, and the opening may be the only substantialflow path out of the interior buffer volume.

In some implementations, each support fin may overlap over 50% of theouter perimeter of one of the wafers when the wafer is in the wafersupport region and supported by the support fin. In some furtherimplementations, each support fin may overlap over 75% of the outerperimeter of one of the wafers when the wafer is in the wafer supportregion and supported by the support fin.

In some implementations, the wafer support region may lie within anannular area with an outer diameter larger than the wafer diameter andan inner diameter within 1″ of the wafer diameter.

In some implementations, the wafer support region of each support finmay be provided by a recessed area in a surface of the support fin thatfaces upwards when the buffer is in use and the recessed area of eachsupport fin may be recessed to a depth that causes a wafer supported bythe support region to be substantially flush with the surface of thesupport fin that faces upwards when the buffer is in use.

In some implementations, the cutout region may have a circular portionof a larger diameter than the wafer, each support fin may have aplurality of pegs extending from a surface of the support fin facing thecenter of the circular portion, and the wafer support region may have anannular area that includes the pegs within its boundaries.

In some implementations, the number of support fins may 24 support fins,25 support fins, 29 support fins, or 30 support fins, or really anynumber of support fins that is desired.

In some implementations, the buffer may include at least one heaterplaten that may be in thermally-conductive contact with at least one ofthe side walls or the back wall.

In some implementations, the buffer may include a plurality of purge gasports, and there may be at least one purge gas port between each pair ofadjacent support fins. In some such implementations, there may be asingle purge gas port between each pair of adjacent support fins andeach purge gas port may have the shape of a long, thin slot running in adirection parallel to the adjacent support fins. In some other suchimplementations, there may be a plurality of purge gas ports betweeneach pair of adjacent support fins. In some such implementations, eachsuch plurality of purge gas ports between each pair of adjacent supportfins may include a linear array of regularly-spaced purge gas ports.

In some implementations, the plurality of purge gas ports may includepurge gas ports located in the back wall. In some other or additionalimplementations, the plurality of purge gas ports may include purge gasports located in at least one side wall.

In some implementations, the buffer may also include a plenum cover anda plenum cavity. The plenum cavity may be defined, at least in part, bythe plenum cover and a surface of the back wall opposite the interiorbuffer volume and the plenum cavity may be in fluidic communication withthe plurality of purge gas ports.

In some implementations, the buffer may also include an exhaust port anda clean air inlet. The clean air inlet may be configured to flow gasacross the opening and into the exhaust port.

In some implementations, an equipment front-end module (EFEM) for asemiconductor processing tool may be provided. The EFEM may include anEFEM housing, one or more loadlocks configured to allow wafers to betransferred from the EFEM to a transfer chamber or process chamber ofthe semiconductor processing tool, one or more mechanical interfaces forsupporting front-opening unified pods (FOUPs), a wafer transfer robotconfigured to transfer wafers between various stations within the EFEM,and one or more of the buffers described above.

Details of one or more implementations of the subject matter describedin this specification are set forth in the accompanying drawings and thedescription below. Other features, aspects, and advantages will becomeapparent from the description, the drawings, and the claims.

DRAWINGS

FIG. 1 depicts an isometric view of an example of a buffer with a singleexit flow direction.

FIG. 2 depicts an isometric exploded view of the buffer of FIG. 1.

FIG. 3 depicts a side section view of the buffer of FIG. 1.

FIG. 4 depicts a detail view of a portion of FIG. 3.

FIG. 5 depicts an isometric section view of the buffer of FIG. 1.

FIG. 6 depicts a plan section view of the buffer of FIG. 1.

FIG. 7 depicts an isometric plan section view of the buffer of FIG. 1.

FIG. 8 depicts a plan section view of the buffer of FIG. 1 without anywafers present.

FIG. 9 depicts an isometric plan section view of the buffer of FIG. 1without any wafers present.

FIG. 10 depicts an isometric view of a buffer installed into a housingthat is configured to direct clean air across the front of the buffer.

FIG. 11 depicts an isometric section view of the buffer and housing ofFIG. 10.

FIG. 12 depicts an isometric exploded section view of the buffer andhousing of FIG. 10.

FIG. 13 depicts a plan view of an EFEM with two buffers installed.

FIG. 14 depicts a top section view of an example buffer similar to thebuffer shown in FIG. 1.

FIG. 15 depicts a top section view of another example buffer.

FIG. 16 depicts a top section view of yet another example buffer.

FIG. 17 depicts a top sectional view of a buffer with a hexagonalcross-section.

FIG. 18 depicts a top sectional view of a buffer with a cylindrical backwall.

FIG. 19 depicts an exploded isometric view of another example of animplementation of a buffer.

FIG. 19′ depicts a detail view of a portion of FIG. 19.

FIG. 20 depicts an isometric section view of the example buffer of FIG.19.

FIG. 21 depicts another isometric section view of the example buffer ofFIG. 19.

FIG. 22 depicts a top section view of the example buffer of FIG. 19.

FIG. 23 depicts a front view of a buffer with a side-mounted exhaust andside-mounted filtered air inlet.

FIG. 24 depicts a front view of a buffer with bottom-mounted exhaust anda top-mounted filtered air inlet.

FIG. 25 depicts a front view of a buffer with top-mounted filtered airinlet and side- and bottom-mounted exhausts.

FIGS. 1 through 22 are drawn to-scale within each Figure, with theexception of the purge gas ports in some of the figures, which have beenincreased in diameter to allow for easier visibility.

DETAILED DESCRIPTION

Examples of various embodiments are illustrated in the accompanyingdrawings and described further below. It will be understood that thediscussion herein is not intended to limit the claims to the specificembodiments described. On the contrary, it is intended to coveralternatives, modifications, and equivalents as may be included withinthe spirit and scope of the invention as defined by the appended claims.In the following description, numerous specific details are set forth inorder to provide a thorough understanding of the present invention. Thepresent invention may be practiced without some or all of these specificdetails. In other instances, well-known process operations have not beendescribed in detail in order not to unnecessarily obscure the presentinvention.

The present inventors have realized that existing buffers may beconsiderably improved in a number of ways. For example, the presentinventors determined that a buffer that is effectively closed off fromthe ambient environment except for the side of the buffer through whichwafers are inserted into (and removed from) the buffer may provide amuch higher purity purge gas environment as compared with traditionalbuffers. In traditional buffers, the front and the back surface of thebuffer are typically open to the ambient environment and purge gas isdirected into the gaps between the wafers stacked within the buffer fromports located on either side of the wafer. The purge gas then flowstowards the middle, front, and back of the wafers and then down intosome form of exhaust system, where it is scrubbed and disposed of.

The present inventors determined that due to the fact traditionalbuffers are largely open structures, e.g., with no back wall, wafersresting in such buffers are inevitably exposed to air from theminienvironment—even if purge gas is injected between the wafers. Thisis because there is always a pressure differential between the front andback sides of such a buffer, and this pressure differential causes airfrom the EFEM to be drawn through the wafer stack (perhaps at a slowoverall rate, but drawn through nonetheless).

The present inventors determined that enclosing the buffer on at leastthree sides eliminates the cross-flow gas contamination issue discussedabove, as there is only one significant entry/exit from the buffer froma bulk gas flow perspective.

The present inventors further determined that supporting the wafers in amanner that provides a substantially unbroken surface extending from thewafers' edges towards the side walls and the back wall of the buffer(assuming that the opening through which the wafers are inserted into orremoved from the buffer is in the “front” of the buffer) may provideenhanced purge gas effectiveness by limiting inter-wafer purge gas flow.Such support may be provided by support fins that extend inwards towardsthe center of the buffer from the side walls and the back wall. Thesupport fins may have a cutout region in the middle that allows a waferhandling robot to insert an end effector into the buffer, move the endeffector in a vertical, upwards direction to lift a wafer up from below,and then retract the end effector and the wafer from the buffer. Thecutout region may thus extend from the opening in the front of thebuffer to a point between the nominal center of mass of the wafers andthe back wall.

The support fins and wafers, when the wafers are resting on the supportfins, each form an effectively continuous shelf that extends from theback wall, along the side walls, and to the front of the buffer. Withoutthe wafers, there would be a large hole in the middle of each supportfin where the cutout region is; the wafers, when present, act to coverthis hole up. The support fin/wafer combination acts to limit verticalmigration of gas within the buffer.

The present inventors also determined that purge gas flowed into thespace above each support fin from linear arrays of purge gas ports inone or more walls of the buffer may flow across the support fin and thewafer supported by the support fin (if present). The purge gas may thusflow in a primarily horizontal direction (with respect to the Earthframe of reference) until it exits the buffer through the openingthrough which the wafers are introduced into the buffer. While the purgegas ports may be located in either or both of the side walls of thebuffer, the present inventors determined that locating purge gas portsin the back wall of the buffer appeared to offer advantageousperformance. Purge gas flowed from the back wall may generally flowdirectly across each wafer towards the opening, i.e., in a single,overall direction, with little risk of dead zones in which purge gas andvolatiles from the wafers may collect and loiter. Generally speaking,the opening (or, more specifically, the boundary formed by the edges ofthe wafers and support fins closest to the opening) may be the onlysubstantial flow path exit out of the interior buffer volume (assumingthat, in cases where the floor of the buffer is open, a wafer is in thebottom-most position in the buffer) for the purge gas that is introducedinto the interior buffer volume. For example, while there may be someincidental leakage of purge gas out of seams or other smallgaps/holes/etc. that may be present in the buffer (e.g., in order toaccommodate various features needed to assemble the buffer), suchincidental gas flow is completely overshadowed by the gas flow out ofthe opening, e.g., on the order of three or more magnitudes less thanthe magnitude of gas flow through the opening. This causes the purge gasthat is introduced into the gap above each wafer to flow across thewafer up to the edge of that wafer closest to the front opening of thebuffer and then be drawn into an exhaust without causing air from theEFEM to be drawn into that same space.

The following discussion is directed at an example implementation of abuffer designed according to these principles. It is to be understoodthat other implementations may be designed differently while stillpracticing some or all of the concepts discussed herein, and the presentdisclosure is not limited to just the implementation shown.

FIG. 1 depicts an isometric view of an example of a buffer with a singleexit flow direction. FIG. 2 depicts an isometric exploded view of thebuffer of FIG. 1.

A buffer 100 is shown in FIGS. 1 and 2. The buffer 100 has a rectangularprismatic shape, although other shapes are possible as well, including abuffer with a semicircular back wall, or a buffer with side walls thattaper together between the back wall and the wafer centers (thus formingmore of a hexagonal shape in the plan view). The buffer 100 has a lid orceiling 106, which in this implementation, includes handles 136 thatprotrude out from the ceiling 106 and allow for easy grasping andhandling of the buffer 100. A pair of heating platens 126 may be inthermally-conductive contact with side walls 102 of the buffer 100 (suchheating platens may also or alternatively located in other positions,e.g., on the ceiling/lid, the floor, the back wall, etc.). The heatingplatens 126 may be used to heat the walls of the buffer and to helpdrive out any moisture that may manage to stray inside of the buffer.Some implementations may forego the inclusion of the heating platens 126if heating is not needed.

The implementation of the buffer 100 that is shown in FIG. 1 isconfigured to flow gas from purge gas ports located in a back wall 104of the buffer 100 into an interior buffer volume 112 and towards anopening 114 in the front of the buffer 100. The purge gas, in thisimplementation, may be distributed to the purge gas ports by way of aplenum cavity 130 that is formed between a plenum cover 128 and the backwall 104. If purge gas ports are additionally or alternatively locatedin the side wall(s) 102 of the buffer 100, a similar plenum structuremay be used on those side walls. Such purge gas may, for example, benitrogen or some other inert gas.

As can be seen in FIG. 2, a plurality of wafers 118 may be stored withinthe buffer 100. In this particular implementation, 25 wafers 118 may bestored in the buffer 100, although other implementations may store othernumbers of wafers 118, e.g., 30 wafers, 35 wafers, etc. The wafers shownhere are 300 mm wafers, although the concepts described herein may beadapted to provide buffers for 450 mm wafers or any other size of wafer.

Also visible in FIG. 1 are a plurality of support fins 110. Each supportfin 102 has a wafer support region that is, in this implementation,C-shaped, with the inside radius of the C being smaller than one halfthe wafer nominal diameter, and the outside radius of the C being largerthan one half the wafer nominal diameter. The wafer support region maybe generally flat or planar, and may typically include three or morewafer support features 140 located at spaced-apart locations in thewafer support region. The wafer support features 140 may serve toelevate the wafer off of the wafer support region such that each wafer118 has minimal contact with the support fin 110 that supports it. Thishelps reduce particulate generation/contamination. The wafer supportregion may, for example, lie within an annular region with an outerdiameter larger than the wafer diameter and an inner diameter that iswithin 1″ of the wafer diameter, although other implementations may havedifferent sized wafer support regions.

In the implementation shown, there are 24 support fins 110 shown. The25^(th) wafer 118 (the bottom-most wafer 118) is supported by a wafersupport region that is part of a floor 108. This last wafer supportregion could just as easily be provided using a 25^(th) support fin 110,however.

The region within the inside radius of the C may be thought of as acutout region with a cutout region throat 144. The cutout region throat144 may be sized so as to be wide enough to allow an end effector of awafer handling robot with which the buffer is to be used to be insertedinto the cutout region via the cutout region throat 144. In someimplementations, the cutout region and the cutout region throat 144 maybe the same width, i.e., having the form of a large slot that travelstowards the back wall 104 from the opening 114. The various componentsshown may be assembled together using any appropriate fasteningtechniques, e.g., threaded fasteners, clips, etc. Such assembly featuresare not necessarily shown in the Figures to avoid undue visual clutter.

FIG. 3 depicts a side section view of the buffer of FIG. 1. FIG. 4depicts a detail view of a portion of FIG. 3. Arrows showing notionalgas flow paths have been added to this view to help illustrate the flowof purge gas in the buffer 100. Purge gas may flow into the plenumcavity 130 that is formed between the plenum cover 128 and the back wall104 from purge gas inlets 142. In this implementation, there are twopurge gas inlets 142 located in a side portion of the plenum cover 128,although more or fewer such purge gas inlets 142 may be used and thelocation or locations of such purge gas inlets may be varied. The purgegas may flow into the plenum cavity 130 and then flow through the backwall 104 through a number of linear arrays of purge gas ports 124. Eachlinear array of purge gas ports 124 may flow gas into the space aboveone of the support fins 110 (and wafer 118, if present). Generally, thewafers 118 may be supported by sequentially adjacent support fins 110,i.e., without empty support fins 110 between the wafers, so that thebottom of each wafer 118 forms a “ceiling” for the space between thewafer 118 and the support fin 110 directly below that wafer 118. This“ceiling” helps constrain the flow of purge gas in a generally lineardirection towards the opening 114. The “ceiling” for the topmost wafer118 in the buffer 100 may be provided by the actual ceiling or lid 106.

In the support fins 110 shown, the wafer support region 116 is formed bya recessed area 122 that allows the wafer 118 to sit below the nominalupper surface of the support fin 110 instead of sitting proud of, orflush with, the upper surface. As can be seen, there is both a radialgap and an axial gap between the wafer 118 and the support fin 110. Theradial gap is to accommodate radial uncertainty in wafer placement bythe robot arm that handles the wafers. The axial gap is to accommodatethe wafer support features 140 and to prevent the wafer 118 fromactually coming into contact with the wafer support region. Purge gasmay, of course, flow through these small gaps and migrate betweendifferent inter-wafer spaces, but the conductance of such gaps iscompletely overshadowed by the conductance of the large passage formedbetween the opening 114 and the back wall 104 between each pair ofadjacent support fins 110. These gaps may typically be on the order of amillimeter or two or less. More specifically, the radial gap may be keptas small as the radial positioning tolerance of the robot arm reasonablypermits. The axial gap may, in some implementations, be reduced to theminimum gap that still provides sufficient clearance to prevent thepossibility of as small as is necessary to keep the wafer 118 fromcontacting the wafer support region (except at the wafer supportfeatures 140). Some implementations of the buffer may provide a wafersupport region without wafer support features, allowing for large-areacontact between the wafer and the wafer support region (this may providefor less gas migration through this interface due to the smaller gapsize, or lack thereof, but at the expense of potentially greatercontaminate production due to the increased contact area).

The buffers described herein may also be implemented without recessedareas (or with recessed areas of shallower depth) such that the wafer118 stands at least slightly proud of the upper surface of thesupporting support fin 110. Such implementations, however, may see anincrease in the amount of purge gas migration between inter-wafer spacessince the flow path between the wafers 118 and the support fins 110 isless tortuous as compared with support fins 110 with recessed areas 122.In yet other implementations, the recess may be sized such that thewafer is substantially flush with the support fin top surface.

As discussed above, while the implementation shown in the accompanyingFigures is designed to prevent or mitigate purge gas flow between thestacked wafers 118, there may still be some such purge gas migration,e.g., via small gaps between the wafers 118 and the wafer supportregions 116. While the example buffer 100 shown in the Figures avoidsincluding features other than the above-mentioned gaps that may allowfor inter-wafer gas flow, some buffer implementations may includeadditional features that allow for inter-wafer gas migration. While suchfeatures are generally undesirable from the perspective of thisdisclosure, there may be other considerations that warrant theirinclusion, e.g., visual or optical inspection considerations, assemblyconsiderations, etc. To that end, while it is generally preferable thateach support fin 110 be without perforations or gaps between the wafersupport region 116 and the back wall 104 and the side walls 102, it isto be understood that implementations where there are small perforationsor gaps in the support fin 110 between the wafer support region 116 andthe back wall 104 and side walls 102 may also fall within the scope ofthis disclosure. In such additional implementations, there may still besubstantially no inter-wafer purge gas flow, i.e., the amount of purgegas flow across each wafer/support fin is at least three orders ofmagnitude or more greater than the amount of inter-wafer purge gas flowfrom that wafer/support fin.

FIG. 5 depicts an isometric section view of the buffer of FIG. 1. Arrowshave also been added to this view to show purge gas flow, although onlyfor three of the wafer/support fin levels (to avoid undueclutter—similar gas flows, however, would occur for each wafer/supportfin level). As can be seen, purge gas flows generally in a lineardirection towards the opening 114. Since the edge of the “shelf” formedby each wafer 118 and its supporting support fin 110 near the openingdoes not form a straight line all the way across due to the cutoutregion throat 144, some of the purge gas may flow off of the support fin110 or wafer 118 into the notch formed by the intersection of the wafer118 outer edge and the edge of the support fin 110 facing the opposingside wall 102.

FIG. 6 depicts a plan section view of the buffer of FIG. 1. FIG. 7depicts an isometric plan section view of the buffer of FIG. 1. One ofthe linear arrays of purge gas ports 124 is clearly visible in FIGS. 6and 7. In this example, there are 10 purge gas ports 124 arranged in anequally-spaced linear array. However, more or fewer such purge gas ports124 may be used. In an extreme case, there may be a single purge gasport that extends across most of the back wall 104, e.g., a long, thinslit through which the purge gas may flow.

FIG. 8 depicts a plan section view of the buffer of FIG. 1 without anywafers present. FIG. 9 depicts an isometric plan section view of thebuffer of FIG. 1 without any wafers present. FIGS. 8 and 9 are includedto more clearly depict the wafer support region, which is indicated inthese Figures by wafer support region 116. Also shown is cutout region120, of which cutout region throat 144 forms a part.

While buffers such as the buffer 100 described above may provide amechanism for protecting wafers 118 from non-inert environments,situating such buffers in a particular manner may provide furtherprotection from contamination. One such particular manner is to situatethe buffer in a housing that is configured to cause filtered air to bedirected across the opening 114 in a direction generally perpendicularto the wafers 118.

FIG. 10 depicts an isometric view of a buffer installed into a housingthat is configured to direct clean air across the front of the buffer.FIG. 11 depicts an isometric section view of the buffer and housing ofFIG. 10. FIG. 12 depicts an isometric exploded section view of thebuffer and housing of FIG. 10.

Grey arrows have been added to FIGS. 10, 11, and 12 to indicate the flowof filtered air. Such air is typically flowed from vents in the ceilingof an EFEM towards exhaust ports located in the floor of the EFEM. Inthe case of the housing 154 (see FIG. 12), the housing 154 is shaped tocontrol the flow of filtered air that is supplied from a clean air inlet134 positioned above the buffer 100 such that the filtered air isprevented from impacting the ceiling or lid 106 of the buffer 100 and isinstead routed down the front of the buffer, across the opening 114.Side baffles 150 and front baffles 152 further serve to shape thefiltered air flow into a column that flows across the opening 114. Thiscolumnar filtered air flow is further encouraged by the addition of anexhaust port 132 located at the base of the opening 114 and extendingseveral inches beyond the front of the buffer 100. The exhaust port 132may be fluidically connected with an interior plenum of the housing (seesection view in FIG. 11); an exhaust grating 146 may be used as a baffleto assist in evening out exhaust flow distribution. The gas that issucked into the exhaust port 132 may be flowed out of an exhaust ventport 148 that delivers the gas to a scrubber system or other safedisposal system. By including an additional exhaust port directly infront of the buffer, columnar flow of filtered air across the opening isencouraged. Such columnar flow has the effect of sucking the purge gasthat flows horizontally off the edge of each “ledge” into a verticalflow column, where it is then evacuated as part of the exhaust stream.This also helps protect the other equipment in the EFEM fromcontamination by chemicals that are entrained in the purge gas.

FIG. 13 depicts a plan view of an EFEM with two buffers installed.Visible in FIG. 13 is EFEM 156, which is designed to accommodate threeFOUPs 158 and which has two buffer units 100, as described herein. Awafer handling robot 160 with an end effector 162 (a single-arm robot isshown, but a multi-arm/multi-end-effector robot or multiple robots maybe used as well, however) may be located within the EFEM 156 and used totransport wafers between the FOUPs 158, the buffers 100, and loadlocks164. The loadlocks 164 may be connected to a transfer chamber or processchamber.

FIG. 14 depicts a top section view of an example buffer similar to thebuffer shown in FIG. 1. A buffer 1400 that has a rectangular (in thiscase, nearly square) cross-sectional profile is shown. The buffer 1400has a back wall 1404, side walls 1402, and an opening opposite the backwall. A support fin 1410 extends from the back wall 1404 and the sidewalls 1402 past the exterior diameter of a wafer 1418 (shown using adashed circle, in this example). In this example, the support fin 1410extends up to a circular cutout region 1420 with a rectangular cutoutregion throat 1444. The cutout region throat 1444 is wide enough toallow an end effector 1462 (dotted outline) of a wafer handling robot(not shown) to be inserted into the buffer 1400. A wafer support region1416 is defined between the outer edge of the cutout region 1420 and acircular boundary around the wafer 1418 and having a diameter at leastas large as the wafer 1418.

FIG. 15 depicts a top section view of another example buffer. A buffer1500 that has a rectangular (in this case, nearly square)cross-sectional profile is shown. The buffer 1500 has a back wall 1504,side walls 1502, and an opening opposite the back wall. A support fin1510 extends from the back wall 1504 and the side walls 1502 past theexterior diameter of a wafer 1518 (shown using a dashed circle, in thisexample). In this example, the support fin 1510 extends up to aslot-shaped cutout region 1520 that has a rounded innermost surface(other shapes are also possible, however, depending on the desires ofthe designer). In this example, the cutout region 1520 has a cutoutregion throat 1544 that is, in essence, the same width as the cutoutregion 1520. The cutout region throat 1544 is wide enough to allow anend effector 1562 (dotted outline) of a wafer handling robot (not shown)to be inserted into the buffer 1500. A wafer support region 1516 isdefined between the outer edge of the cutout region 1520 and a circularboundary around the wafer 1518 and having a diameter at least as largeas the wafer 1518.

FIG. 16 depicts a top section view of yet another example buffer. Abuffer 1600 that has a rectangular (in this case, nearly square)cross-sectional profile is shown. The buffer 1600 has a back wall 1604,side walls 1602, and an opening opposite the back wall. A support fin1610 extends from the back wall 1604 and the side walls 1602 past theexterior diameter of a wafer 1618 (shown using a dashed circle, in thisexample). In this example, the support fin 1610 extends up to aslot-shaped cutout region 1620 that has a rounded innermost surface(other shapes are also possible, however, depending on the desires ofthe designer). As with the previous example buffer 1500, the cutoutregion 1620 has a cutout region throat 1644 that is, in essence, thesame width as the cutout region 1620. The cutout region throat 1644 iswide enough to allow an end effector 1662 (dotted outline) of a waferhandling robot (not shown) to be inserted into the buffer 1600. In thisexample, however, the end effector is wider than in the prior example,and the cutout region throat 1644 is just slightly smaller than thediameter of the wafer 1618. A wafer support region 1616 is definedbetween the outer edge of the cutout region 1620 and a circular boundaryaround the wafer 1618 and having a diameter at least as large as thewafer 1618. The wafer support region 1616 only overlaps with just over50% of the outer perimeter of the wafer 1618, as compared with the wafersupport region 1516's overlap with over 75% of the outer perimeter ofthe wafer 1518, but such a reduced overlap may still provide acceptableperformance according to the principles discussed herein.

As discussed previously, while the example buffers discussed above haveprimarily had rectangular cross-sections in the plan view, buffers withother cross-sectional profiles may also be implemented using thetechniques discussed herein.

FIG. 17 depicts a top sectional view of a buffer with a hexagonalcross-section. Such a buffer 1700 may be provided, as illustrated, bychamfering a back wall 1704 such that the back corners of the buffer1700 are removed (or at least replaced with corners greater than 90degrees in included angle). Side walls 1702 may, in such designs, onlyextend a small distance beyond the center of whatever wafers areinserted into the buffer 1700. This may have the effect of reducing thesurface area of support fin 1710 (the cutout region 1720, cutout regionthroat 1744, and wafer support region 1716 are substantially identical,in this case, to the corresponding structures in FIG. 14), and mayreduce the amount of dead space that is present in the buffer 1700.

FIG. 18 depicts a top sectional view of a buffer with a cylindrical backwall. Such a buffer 1800 may be provided, as illustrated, by shaping aback wall 1804 such that it is the shape of a half-cylinder. Side walls1802 may, in such designs, only extend a small distance beyond thecenter of whatever wafers are inserted into the buffer 1800. Such animplementation may further act to reduce the potential dead space withinthe buffer 1800 as compared with buffer 1700 (the cutout region 1820,cutout region throat 1844, and wafer support region 1816 are, as withthe prior example, substantially identical to the correspondingstructures in FIG. 14).

FIGS. 14 through 18 represent only some of the different ways that theconcepts and principles discussed herein may be implemented to provide abuffer. It is to be understood that other implementations may departfrom the depicted examples but still fall within the scope of thisdisclosure, and that this disclosure is not to be limited to only theexamples provided.

The side walls, back wall, and support fins of buffers designedaccording to the principles discussed herein may be manufactured in anumber of different ways. For example, the side walls, back wall, andsupport fins may be cast as a single, monolithic part and the purge gasports and wafer support features may then be machined into the castpart. In another implementation, the side walls, back wall, and supportfins may be assembled by stacking together a large number of horizontalcross-sectional pieces, e.g., horizontal cross-sections of the sidewalls and back wall without the support fins alternating with horizontalcross-sections of the side walls and back wall with the support fins.This may allow the buffer to be expanded or reduced in size withoutneeding to produce an entirely new buffer (further cross-sectionalpieces may be added or cross-sectional pieces removed to increase ordecrease the number of wafers that may be supported within the buffer).These, and other, manufacturing techniques may be used to construct theside walls, back wall, and support fin structures. The buffer structuresmay be made of any suitable material, such as, for example, an aluminumalloy. The wafer support features may be provided by small featuresmachined into the support fins, or by small components attached to thesupport fins, e.g., pins, standoffs, or small, stainless steel ballsthat are press-fit into holes in the support fins.

FIGS. 19 through 22 depict another example of a buffer embodying theconcepts discussed herein. FIG. 19 depicts an exploded isometric view ofthis second example buffer. FIG. 20 depicts an isometric section view ofthe example buffer of FIG. 19. FIG. 21 depicts another isometric sectionview of the example buffer of FIG. 19. FIG. 22 depicts a top sectionview of the example buffer of FIG. 19.

Visible in FIGS. 19 through 22 is buffer 2100, which has a shape similarto the buffer of FIG. 1700. As can be seen, the buffer 2100 has two sidewalls 2102 and a back wall 2104 with three segments (one perpendicularto the side walls 2102, and flanking segments at 45 degrees to the sidewalls 2102), as well as a floor 2108 and a ceiling 2106.

In this implementation, all of the side walls 2102 and back wall 2104contain plenum cavities 2130, which are capped by plenum covers 2128.Each plenum cavity 2130 has a plurality of purge gas ports 2124; thepurge gas ports 2124 are arranged such that purge gas is directed fromsubsets of the purge gas ports 2124 between each pair of wafers 2118.The wafers 2118 may be supported on pegs 2144 that project radiallyinward from the interior surface of support fins 2110.

The buffer 2100 is different from the buffer 100 in that there is anexhaust port 2132 located in the floor 2108, rather than in front of thebuffer. However, just like in the buffer 100, purge gas that isintroduced into the inter-wafer spaces through the purge gas ports 2124is constrained by the wafers 2118 and the support fins 2110 such that itflows towards the opening 2114 (the opening 2114 is indicated in higherfidelity than the opening 114, which is represented in the simplifiedform of a plane). This prevents ambient air from the surroundingenvironment from being drawn into the inter-wafer spaces. The purge gas,after reaching the edge of the wafers closest to the opening 2114, isthen drawn downwards (essentially along the opening 2114 boundary)towards the exhaust port 2132. Any residuals from the wafers 2118 thatare entrained in the purge gas will thus be drawn into the exhaust port2132.

As is visible in the detail view FIG. 19′, the support fins 2110 inbuffer 2100 are of a slightly different design than in buffer 100. Inbuffer 2100, the cutout region 2120 (see FIG. 22) has a circular portionthat is slightly larger in diameter than the wafer 2118, resulting in asmall radial gap between the support fins 2110 and the wafer 2118 aboutthe periphery of the wafer 2118. Instead of being supported by restingon the upper surface of the support fin 2110, wafers 2118 may besupported by pegs 2144 that protrude into the cutout region 2120 fromthe interior surface of the support fins 2110. The pegs 2144 may includea rod portion with an expanded-diameter portion, e.g., a spherical knob,that is designed to contact the wafers 2118. As can be seen, the radialgaps formed between the wafers 2118 and the support fins 2110 offer aless tortuous path than the wafer support region of the support fins110. However, the bulk of the purge gas flow within the buffer 2100 willstill be towards the opening 2114.

In such an implementation, the wafer support region may be viewed asbeing an annular area that includes the pegs 2144 within its area.

It is also to be understood that the buffers described herein may becombined with various configurations of filtered air and exhaustsystems. Furthermore, it is to be understood that the “filtered air” mayalso be replaced with other gases, e.g., an inert gas (at least, from awafer chemistry standpoint) such as nitrogen may be supplied via thefiltered or clean “air” inlet, forming a curtain of purge gas in frontof the buffer opening. Following are a several, non-exhaustive examplesof potential filtered air inlet/exhaust port configurations that may beused.

FIG. 23 depicts a front view of a buffer with a side-mounted exhaust andside-mounted filtered air inlet. As can be see, in this configuration, aclean air (or purge gas) curtain flows across buffer 2300 from filteredair inlet 2334 to exhaust port 2332 (left to right); the direction, ofcourse, may also be reversed from the direction shown, if desired. Iftwo buffers 2300 are located adjacent to one another, then the filteredair inlet 2334 may be interposed between them and exhaust ports 2332 maybe placed on opposing sides of the buffers 2300, allowing a commonfiltered air inlet 2334 to provide a gas curtain across two separatebuffers 2300.

FIG. 24 depicts a front view of a buffer with bottom-mounted exhaust anda top-mounted filtered air inlet. This implementation, in which filteredair (or purge gas) is flowed from a filtered air inlet 2434 mountedabove a buffer 2400 into an exhaust port 2432 mounted below the buffer2400, corresponds generally with the arrangement shown in FIGS. 10through 12.

FIG. 25 depicts a front view of a buffer with top-mounted filtered airinlet and side- and bottom-mounted exhausts. Finally, as can be seen inFIG. 25, another configuration that may be used is to have both side-and bottom-mounted exhaust ports 2532 draw air from a top-mountedfiltered air inlet 2534. This may prove to provide an even moreeffective barrier against accidentally drawing EFEM mini-environment airinto the buffer 2500.

It is to be understood that the buffers and housings described above mayalso include other or additional components, e.g.,centering/buffer-locating features, temperature sensors, humiditysensors, etc. For example, a buffer such as those described herein maybe implemented so as to be easily removable from an EFEM for rapidinspection and cleaning (or replacement), and may have features on theunderside of the floor that allow the EFEM to be rapidly positioned withrespect to the EFEM.

The use of relative positioning terms such as “above” and “below” withinthis specification are used in their typical senses. The term “front,”when used with respect to the buffer, refers to the portion of thebuffer through which wafers are inserted during normal use. The term“back” refers to the portion of the buffer on the opposite side from thefront.

It will also be understood that unless features in any of the particulardescribed implementations are expressly identified as incompatible withone another or the surrounding context implies that they are mutuallyexclusive and not readily combinable in a complementary and/orsupportive sense, the totality of this disclosure contemplates andenvisions that specific features of those complementary implementationscan be selectively combined to provide one or more comprehensive, butslightly different, technical solutions. It will therefore be furtherappreciated that the above description has been given by way of exampleonly and that modifications in detail may be made within the scope ofthe invention.

What is claimed is:
 1. An apparatus for storing multiple wafers in asemiconductor manufacturing tool, the apparatus comprising: a bufferthat includes two opposing side walls, a back wall; and a plurality ofsupport fins; at least one heater platen, the at least one heater platenin thermally-conductive contact with at least one of the opposing sidewalls; an exhaust port; and a clean air inlet, wherein: the two opposingside walls and the back wall define part of an interior buffer volume;the interior buffer volume is partially bounded by an opening oppositethe back wall; the clean air inlet is configured to flow gas across theopening and into the exhaust port; the clean air inlet and the exhaustport are both positioned outside of the interior buffer volume and suchthat the opening is interposed between the interior buffer volume andthe clean air inlet; the opposing side walls are between the opening andthe back wall; and each support fin: a) extends from the back wall,along both side walls, and to the opening, b) is substantially flat andhorizontal when the buffer is in use, c) has a wafer support region thatis smaller in diameter than the wafers with which the buffer is designedto be used, d) extends from the side walls and the back wall in asubstantially unbroken manner up to at least the wafer support region,and e) has a cutout region that extends from the opening past the centerof the wafer support region and that is wide enough in a directiontransverse to the opening to allow an end effector of a wafer handlingrobot to place a wafer on the support fin.
 2. The apparatus of claim 1,wherein: each support fin is offset from the adjacent support fin orsupport fins, and the support fins form a vertical linear array when thebuffer is in use.
 3. The apparatus of claim 1, wherein the bufferfurther includes: a ceiling; and a floor, wherein: the interior buffervolume is further defined by the ceiling and the floor, and the backwall and the two opposing side walls are between the ceiling and thefloor.
 4. The apparatus of claim 3, wherein: the opposing side walls,the back wall, the ceiling, and the floor seal the interior buffervolume off from the surrounding environment; and the opening is the onlysubstantial flow path out of the interior buffer volume.
 5. Theapparatus of claim 1, wherein each support fin overlaps over 50% of theouter perimeter of one of the wafers when the wafer is in the wafersupport region and supported by the support fin.
 6. The apparatus ofclaim 1, wherein each support fin overlaps over 75% of the outerperimeter of one of the wafers when the wafer is in the wafer supportregion and supported by the support fin.
 7. The apparatus of claim 1,wherein the wafer support region lies within an annular area with anouter diameter larger than the wafer diameter and an inner diameterwithin 1″ of the wafer diameter.
 8. The apparatus of claim 1, wherein:the wafer support region of each support fin is provided by a recessedarea in a surface of the support fin that faces upwards when the bufferis in use; and the recessed area of each support fin is recessed to adepth that causes an upper surface of a wafer supported by the supportregion to be flush with an upper surface of the support fin when thebuffer is in use.
 9. The apparatus of claim 1, wherein: the cutoutregion has a circular portion of a larger diameter than the wafer, eachsupport fin has a plurality of pegs extending from a surface of thesupport fin facing the center of the circular portion, and the wafersupport region is an annular area that includes the pegs within itsboundaries.
 10. The apparatus of claim 1, wherein the plurality ofsupport fins is selected from the group consisting of: 24 support fins,25 support fins, 29 support fins, and 30 support fins.
 11. The apparatusof claim 1, further comprising at least one additional heater platen,the at least one additional heater platen in thermally-conductivecontact with the back wall.
 12. The apparatus of claim 1, furthercomprising a plurality of purge gas ports, wherein there is at least onepurge gas port between each pair of adjacent support fins.
 13. Theapparatus of claim 12, wherein there is a single purge gas port betweeneach pair of adjacent support fins and each purge gas port has the shapeof a long, thin slot running in a direction parallel to the adjacentsupport fins.
 14. The apparatus of claim 12, wherein there is aplurality of purge gas ports between each pair of adjacent support fins.15. The apparatus of claim 14, wherein each plurality of purge gas portsbetween each pair of adjacent support fins includes a linear array ofregularly-spaced purge gas ports.
 16. The apparatus of claim 14, whereinthe plurality of purge gas ports includes purge gas ports located in theback wall.
 17. The apparatus of claim 14, wherein the plurality of purgegas ports includes purge gas ports located in at least one side wall.18. The apparatus of claim 16, further comprising: a plenum cover; aplenum cavity, wherein: the plenum cavity is defined, at least in part,by the plenum cover and a surface of the back wall opposite the interiorbuffer volume, and the plenum cavity is in fluidic communication withthe plurality of purge gas ports.
 19. An equipment front-end module(EFEM) for a semiconductor processing tool, the EFEM comprising: an EFEMhousing; one or more loadlocks configured to allow wafers to betransferred from the EFEM to a transfer chamber or process chamber ofthe semiconductor processing tool; one or more mechanical interfaces forsupporting front-opening unified pods (FOUPs); a wafer transfer robotconfigured to transfer wafers between various stations within the EFEM;and one or more of the apparatuses of claim
 1. 20. An apparatus forstoring multiple wafers in a semiconductor manufacturing tool, theapparatus comprising: a buffer that includes two opposing side walls, aback wall, and a plurality of support fins; at least one heater platen,the at least one heater platen in thermally-conductive contact with atleast one of the opposing side walls; an exhaust port; and a clean airinlet, wherein: the two opposing side walls and the back wall definepart of an interior buffer volume; the interior buffer volume ispartially bounded by an opening opposite the back wall; the clean airinlet is configured to flow gas in a first direction across the openingand into the exhaust port and is positioned such that the opening isinterposed between the interior buffer volume and the clean air inlet;the first direction is nominally parallel to the side walls and the backwall; the opposing side walls are between the opening and the back wall;and each support fin: a) extends from the back wall, along both sidewalls, and to the opening, b) is substantially flat and horizontal whenthe buffer is in use, c) has a wafer support region that is smaller indiameter than the wafers with which the buffer is designed to be used,d) extends from the side walls and the back wall in a substantiallyunbroken manner up to at least the wafer support region, and e) has acutout region that extends from the opening past the center of the wafersupport region and that is wide enough in a direction transverse to theopening to allow an end effector of a wafer handling robot to place awafer on the support fin.